The spinal column is a highly complex system of bones and connective tissues that provides support for the body and protects the delicate spinal cord. The spinal column includes a series of vertebrae stacked one on top of the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. The vertebrae in the cervical, thoracic, and lumbar regions of the spine are separated by intervertebral discs, which serve as cushions between adjacent vertebrae to dampen compressive forces experienced by the spine. A vertebral canal containing the spinal cord is formed by the intervertebral foramen of the vertebrae.
There are many types of conditions that can lead to significant pain and affect movement of the spine. Oftentimes these conditions are treated by securing or more implants to the spine, with the implants being designed to achieve a particular type of treatment. For instance, facet implants are often implanted between the facet surfaces of adjacent vertebrae when it is desired to provide joint spacing, joint stabilization, joint capsule replacement, cushioning and/or an articulating surface for the opposing pair of facets. Examples of such facet implants are disclosed in U.S. patent application Ser. Nos. 11/221,938 and 11/274,385, which are owned by the assignee of the present application and hereby incorporated by reference in their entirety. Other implants include, without limitation: cervical plates, fixation rods, and similar devices.
The implants are typically secured to the spine using one or more bone screws or other attachment members. Other fixation techniques are also used when desired. For example, in some applications the implants are secured using adhesive or sutures. In other applications, the implants are secured by a post cemented into a cavity created in the bone. Although a wide variety of attachment devices and methods exist, there remains room for improvement.